(1) Field of the Invention
This invention relates generally to extrusion machines, and more particularly to roller head die arrangements which are adaptable to the discharge ends of extrusion machines.
(2) Prior Art
An extrusion machine with a roller die arrangement may comprise an extruding device in which material is mixed and propelled along the length of a cylinder or barrel, then discharged through an opening in the extrusion machine, where it is introduced between cooperating calender rolls which calender the material to the desired thickness. The process through the extrusion machine begins with the material being dumped from a mixing machine, into a hopper of the extruding machine where it is forced along the length of the extruder barrel by interaction with a rotating screw arrangement supported therewithin. The material is discharged from the extruder barrel in a plastic state under sufficient pressure into the calender rolls which calender the material into a web or sheet. The material is introduced to the rolls in a generally undefined or bulk state.
After completion of the process, any material remaining in the discharge opening and barrel of the extruder machine must be removed since, if it is permitted to stay in the machine, it may degrade, causing contamination of newly produced material, or it may solidify and cause damage to the machine, during subsequent use thereof. Movement of the calender rolls away from the discharge opening would facilitate the cleaning operation. This however, might involve support apparatus and the like for moving the extruder and the rolls apart, as suggested in U.S. Pat. No. 3,895,898. A roller die unit mounted on rails for moving away from the extruder is shown in U.S. Pat. No. 3,274,645 to Chase, and assigned to the assignee of the present invention. Other art showing the roller dies attached to the floor but movable at least partially away from the extruder, is shown in U.S. Pat. No. 3,115,672.
U.S. Pat. No. 3,947,201 to Ellwood, and assigned to the assignee of the present invention shows an extruding and plastic forming apparatus which governs the rate of extrusion flow depending upon feedback from sensors near the rolls. U.S. Pat. No. 4,256,448 to Carle, and also assigned to the assignee of the present invention shows an arrangement of cylinder rolls adapted on a rigid frame attached to an extrusion machine, wherein the rolls are biased obtusely to the direction of plastic flow, permitting non-orthogonal movement of the rolls during high volume flow to permit excess bypass therethrough, and during cleaning of the machine to permit removal of the screw.
There is however, a need for simpler construction of roll supports, which can even permit roll rotation at the point of maximum displacement from one another.
There is also a need for a roller die apparatus which can automatically rapidly compensate and adjust itself for variations in the pumping rate of the extruder without otherwise producing excessive stock pressures between the extruder and the roller die which might damage the machine, without utilizing failure prone electronic circuits.